There are two underlying issue that motivated the disclosed inventions. The first was to improve capabilities for finding special nuclear materials (SNM). The second was to develop potential approaches to improve the capabilities for characterizing or assessing SNM. To get the most information from a radiation field for both of those goals, the ideal sensor would need to discriminate against all forms of background as well as measure energy spectra and image the location of the radiation. The present invention represents an attempt to develop this ideal sensor system and to meet these goals concurrently.
Cost is an issue however the need is great enough and value acceptable. The cost of this type of unique development is likely to be much less than that which has already gone into helium-3 replacement technologies to date and is currently is being spent on scintillator improvements. The technology also offers functionality not provided by current alternatives.
Current neutron detection technology is primarily focused on bulk thermal neutron detectors such as commercial helium-3 tubes or fast neutron detection utilizing liquid or plastic scintillators. Helium-3 detectors are less desirable because of the limited supply of helium-3. Additionally, current helium-3 detectors are bulky and, aside from gaseous electron multipliers (GEMs), the helium-3 proportional tubes do not routinely generate two dimensional information. Multiwire helium-3 proportional detectors have been investigated, but these use a lot of the helium-3 gas and can be difficult to field.
Liquid scintillators have disadvantages in that they are gamma sensitive, the liquids are often flammable and they require bulky photomultiplier tubes. They can discriminate between neutrons and gammas at up to 10 MHz in a laboratory environment, but in intense short-pulsed situations, such as that encountered in active detection, pulse shape discrimination may not be fast enough to acquire the data and resolve gamma background from neutron signals. Liquid scintillators (many of which do not provide pulse shape discrimination against gammas) can be made pixelated, but offer no capability for spectral or angular discrimination without the need for a heavy shield or aperture system.
Exemplary embodiments of the present invention may improve gamma rejection and reduce the consumption of helium-3, as well as providing for increased resolution and directional discrimination. These and other advantages of the present invention may be understood by those skilled in the art from the following detailed description.